Chances for a record remain Thursday. The National Weather Service forecasts a high of 96 degrees. The heat index could reach 105.

With a large high-pressure system hovering over the eastern half of the country, heat advisories stretched from Northern Virginia to Maine. Temperatures reached the mid- to upper-90s in Washington, Philadelphia, New York and Boston.

Wednesday was the hottest day at BWI since Aug. 1 last year, when the temperature reached 99 degrees. The heat prompted Baltimore to open all 11 of its air-conditioned "cooling centers" at 9 a.m. to give residents a place to cool off and get water if they were walking around the city.

The centers, which will also be open Thursday, automatically open if the forecast heat index is above 105 degrees. They can also be opened if the index falls just below that number and if air quality is seen as dangerous, said Brian Schleter, spokesman for the Baltimore City Health Department.

Officials had forecast a Code Orange air-quality day for both Wednesday and Thursday, and are urging smog-sensitive individuals to limit their time outside.

Senior citizens especially are encouraged to visit the cooling centers. According to the city, 80 percent of last year's heat-related deaths were people ages 55 or older. However, they are advised to avoid going outside at all if it isn't necessary.

"We don't encourage them to come out because most of them walk to our center," said Rita Arrington, project director at the Allen Senior Center in Federal Hill.

Arrington said the center sends outreach workers to the homes of seniors identified as at risk. Several other centers throughout the city are open so seniors who don't have air conditioning have a place to escape the heat, she said.

Baltimore Gas and Electric Co. reported few problems Wednesday and will "obviously be preparing for tomorrow, monitoring our system's conditions," said Rob Gould, a spokesman for the utility.

The heat brought Olivia Erhardt, 6, and her mother, Cat, to the Stoneleigh pool in Baltimore County on Wednesday afternoon. The two splashed back and forth, floating on inner tubes.

"It's our go-to place when it's hot," Cat Erhardt said. "When it's not, we go to the movies and play dates with other friends."

At Five Oaks pool in Catonsville, Dan Shaw and his sons, Brendan, 7, and Nick, 5, wrestled in the shallow end, surrounded by about 100 other swimmers fighting off the heat.

"On a hot day, this is the way to go," Shaw said. "It's the only way to beat the heat. Of course, they use me like a jungle gym for an hour and a half and wear me out anyway."

Barbara Bates, Five Oaks' manager, said attendance skyrockets on especially hot summer days. She said she keeps an eye on the daily forecasts and staffs the pool based on the expected attendance — several hundred on a hot day like Wednesday or Thursday.

"You can tell it's hot, because they have their umbrellas up," Bates said. "They normally want the sun, but today they said 'Miss Barb, can we put up the umbrellas?'"

While the guards at Five Oaks and other county pools had their hands full Wednesday, city public pools remained closed. The pools have been open on weekends since Memorial Day but aren't scheduled to be open for everyday use until next week, according to Gwendolyn Chambers, spokeswoman for Baltimore City Recreation and Parks.

The heat was blistering near the Baltimore Beltway's Liberty Road exit, but Tom Matter, a construction worker who commutes from Thurmont, remained cool. His seat in an excavator is enclosed — and, more importantly, air-conditioned.

"I don't share my machine," he said with a laugh. "You're crazy if you think I'm getting out of here."

Foreman Michael Gawlik said he's planning to keep his workers in the shade, working under the Liberty Road overpass, for some shelter from the sun Thursday.

"It depends on what the superintendent wants, but as of right now, my butt's going back under that bridge," he said.